Asymmetrical electrolyte, conductivity

The latter authors used anode and cathode symmetrical cells in EIS analysis in order to simplify the complication that often arises from asymmetrical half-cells so that the contributions from anode/ electrolyte and cathode/electrolyte interfaces could be isolated, and consequently, the temperature-dependences of these components could be established. This is an extension of their earlier work, in which the overall impedances of full lithium ion cells were studied and Ret was identified as the controlling factor. As Figure 68 shows, for each of the two interfaces, Ra dominates the overall impedance in the symmetrical cells as in a full lithium ion cell, indicating that, even at room temperature, the electrodic reaction kinetics at both the cathode and anode surfaces dictate the overall lithium ion chemistry. At lower temperature, this determining role of Ra becomes more pronounced, as Figure 69c shows, in which relative resistance , defined as the ratio of a certain resistance at a specific temperature to that at 20 °C, is used to compare the temperature-dependences of bulk resistance (i b), surface layer resistance Rsi), and i ct- For the convenience of comparison, the temperature-dependence of the ion conductivity measured for the bulk electrolyte is also included in Figure 69 as a benchmark. Apparently, both and Rsi vary with temperature at a similar pace to what ion conductivity adopts, as expected, but a significant deviation was observed in the temperature dependence of R below —10 °C. Thus, one... 

Another interesting work conducted by Wamser and co-workers in the field of porphyrin monomer sensitizers is the functionalization of tetraphenylporphyrin at the para positions of -phenyl with one amino group and three carboxylic acid groups. The resulted asymmetrical porphyrin (45) can be successfully fabricated into a modified solid Gratzel type cell with polyaniline as the solid electrolyte. The overall energy conversion efficiency of this cell is about 2% with a number of opportunities to optimize the efficiency remaining [81]. 

Valve metals — Metals that form a compact, electronic insulating passive layer when anodized in aqueous electrolyte, exhibiting asymmetric conductivity blocking anodic reactions, except at very high voltages. Valve metals include aluminum, - titanium, tantalum, zirconium, hafnium, and niobium. Some other metals, such as tin, may exhibit valve-metal properties under specific conditions. 

FIGURE 6.10 Different membrane concepts for oxygen-ion conducting membranes, (a) Dense mixed conducting membrane top-layer supported on an asymmetric macroporous support (b) dense self-supported mixed conducting membrane with graded porous interfaces and (c) solid electrolyte cell (oxygen pump). 

Fig. 10.1. Different membrane concepts incorporating an oxygen ion conductor (a) mixed conducting oxide, (b) solid electrolyte cell (oxygen pump), and (c) dual-phase membrane. Also shown is the schematics of an asymmetric porous membrane (d), consisting of a support, an intermediate and a barrier layer having a graded porosity across the membrane.

Taking into account the underestimated advantages to operate in aqueous electrolyte, it seems also important to look for other applications of carbon materials where the unique combination of electrical conductivity, surface functionality and porous texture may be useful. Such applications as electrochemical hydrogen storage [116, 117], asymmetric supercapacitors [118] open future perspectives where aU the information previously collected on other systems will be useful. 

The WLF formula shows that the ionic conductivity of the polymer electrolyte is shown in the temperature range higher than Tg. Ionic conductivity decreases rapidly if its temperature goes below that of Tg. The EO unit is recognized as the most excellent structure from the ionic dissociation viewpoint. The ion is transported coupled with the oxyethylene chain motion in amorphous polymer domain. However, oxyethylene structure easily becomes crystalline. Therefore, in order to accelerate the quick molecular motion of the polymer chain and quick ion diffusion, it is important to lower the crystallization of polymer matrixes. The methods for inhibiting the crystallization of the polymer are, for example, to introduce the polyethylene oxide chain into the low Tg polymer such as polysiloxane and phosp-hazene, or to introduce the asymmetric units such as ethylene oxide/propylene oxide (EO/PO) into polymer main chain. 

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